1/* mpz_setbit -- set a specified bit. 2 3Copyright 1991, 1993-1995, 1997, 1999, 2001, 2002, 2012 Free Software 4Foundation, Inc. 5 6This file is part of the GNU MP Library. 7 8The GNU MP Library is free software; you can redistribute it and/or modify 9it under the terms of either: 10 11 * the GNU Lesser General Public License as published by the Free 12 Software Foundation; either version 3 of the License, or (at your 13 option) any later version. 14 15or 16 17 * the GNU General Public License as published by the Free Software 18 Foundation; either version 2 of the License, or (at your option) any 19 later version. 20 21or both in parallel, as here. 22 23The GNU MP Library is distributed in the hope that it will be useful, but 24WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 25or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 26for more details. 27 28You should have received copies of the GNU General Public License and the 29GNU Lesser General Public License along with the GNU MP Library. If not, 30see https://www.gnu.org/licenses/. */ 31 32#include "gmp-impl.h" 33 34void 35mpz_setbit (mpz_ptr d, mp_bitcnt_t bit_idx) 36{ 37 mp_size_t dsize = SIZ (d); 38 mp_ptr dp = PTR (d); 39 mp_size_t limb_idx; 40 mp_limb_t mask; 41 42 limb_idx = bit_idx / GMP_NUMB_BITS; 43 mask = CNST_LIMB(1) << (bit_idx % GMP_NUMB_BITS); 44 if (dsize >= 0) 45 { 46 if (limb_idx < dsize) 47 { 48 dp[limb_idx] |= mask; 49 } 50 else 51 { 52 /* Ugh. The bit should be set outside of the end of the 53 number. We have to increase the size of the number. */ 54 dp = MPZ_REALLOC (d, limb_idx + 1); 55 SIZ (d) = limb_idx + 1; 56 MPN_ZERO (dp + dsize, limb_idx - dsize); 57 dp[limb_idx] = mask; 58 } 59 } 60 else 61 { 62 /* Simulate two's complement arithmetic, i.e. simulate 63 1. Set OP = ~(OP - 1) [with infinitely many leading ones]. 64 2. Set the bit. 65 3. Set OP = ~OP + 1. */ 66 67 dsize = -dsize; 68 69 if (limb_idx < dsize) 70 { 71 mp_size_t zero_bound; 72 /* No index upper bound on this loop, we're sure there's a non-zero limb 73 sooner or later. */ 74 zero_bound = 0; 75 while (dp[zero_bound] == 0) 76 zero_bound++; 77 78 if (limb_idx > zero_bound) 79 { 80 mp_limb_t dlimb; 81 dlimb = dp[limb_idx] & ~mask; 82 dp[limb_idx] = dlimb; 83 84 if (UNLIKELY ((dlimb == 0) + limb_idx == dsize)) /* dsize == limb_idx + 1 */ 85 { 86 /* high limb became zero, must normalize */ 87 MPN_NORMALIZE (dp, limb_idx); 88 SIZ (d) = -limb_idx; 89 } 90 } 91 else if (limb_idx == zero_bound) 92 { 93 dp[limb_idx] = ((dp[limb_idx] - 1) & ~mask) + 1; 94 ASSERT (dp[limb_idx] != 0); 95 } 96 else 97 { 98 MPN_DECR_U (dp + limb_idx, dsize - limb_idx, mask); 99 dsize -= dp[dsize - 1] == 0; 100 SIZ (d) = -dsize; 101 } 102 } 103 } 104} 105